The invention relates to a method for the manufacture of sections of fiber-plastic compound materials by means of at least one draw nozzle in which fibers impregnated with flowable plastic are formed under pressure to a product with a predetermined cross-section and consolidated by the withdrawal of heat. A plant for carrying out the method is disclosed.
By means of a continuous process, which is called pultrusion, sections can be manufactured of reinforcement fibers which are impregnated with plastics (see e.g. V. Kerbiriou xe2x80x9cImprxc3xa4gnieren und Pultrusion von thermoplastischen Verbundprofilenxe2x80x9d , VDI-Verlag, Dxc3xcsseldorf 1997). The plastic is distributed between the fibers in the method in such a manner that a tight, pore-poor polymer matrix arises. The matrix consists of the plastic (matrix polymer) in the form of a largely homogeneous phase that is embedded between the fibers. As a starting product (semi-finished product) one advantageously uses bandlets, mixed fibers, powder impregnated fiber bundles or fiber bundles which are impregnated with flowable plastic which are manufactured from a compound material and which are already consolidated. Thermoplastics or duromers (to the extent that these are not yet hardened and are thus flowable) come under consideration for matrix polymers. In the pultrusion of compound materials with solid thermoplastics, for example the named bandlets, the plastics must first be melted. The fusion viscosity amounts to about 500 to 1000 Pa s. Known draw off speeds through a nozzle of the compound materials can be to up to 6 m/min. Greater speeds lead to losses in the pultrate quality as a result of faulty compression, insufficient distribution of the matrix polymer and/or fiber breakage.
A plant for carrying out a pultrusion comprises a supply device for the starting product, an oven, a nozzle (draw or shaping nozzle) and a draw off device, with the nozzle having a continuously narrowing cross-section in a shape-imparting region. The nozzle is slightly overfilled with the starting product so that a matrix flow-back within the fiber bed that is formed by the fibers takes place. The permeability of the fiber bed is anisotropic. The matrix flow takes place mainly along the fibers, but also transverse to the latter, through which the largely homogeneous distribution of the matrix polymer over the entire cross-section of the section that is to be achieved first results. Due to the matrix flow-back the fiber volume proportion increases in the nozzle and a surplus of plastic forms at the nozzle entry, which drips off there.
The object of the invention is to provide a method for the manufacture of sections of fiber-plastic compound materials, which permits a substantially higher production rate in comparison with known pultrusion methods. This object is satisfied in that the cross-sectional surface of the draw nozzle is periodically increased and decreased in time in its entire shape imparting region, with a value for the frequency of the oscillating cross-sectional surface being chosen to be less than 1 kHz, preferably less than 100 Hz.
The method for the manufacture of profiles of fiber-plastic compound materials is carried out by means of at least one draw nozzle. In this nozzle, fibers that are impregnated with flowable plastic are shaped under pressure to a product with a predetermined cross-section and consolidated with the withdrawal of heat. The cross-sectional surface of the draw nozzle is periodically increased and decreased in time in its entire shape imparting region, with a value for the frequency of the oscillating cross-sectional surface being chosen to be less than 1 kHz, preferably less than 100 Hz.
Various advantageous embodiments of the method in accordance with the invention are disclosed. A plant for carrying out the method is disclosed.
In the course of the method in accordance with the invention, phases during which the pressing is done with a narrow nozzle cross-section alternate periodically with phases during which the nozzle cross-section is expanded so that the pressing pressure is strongly reduced. At the beginning of the pressing phase the matrix component is relatively large; it subsequently decreases due to a matrix flow-back which is caused by the pressing. During the pressing phase the draw off forces are substantially lower in comparison with the known pultrusion when the comparison is made at the same draw off speeds. Therefore a greater draw off speed can be chosen in the method in accordance with the invention at which the draw off forces are just as large as in the known pultrusion. Also, at a thus increased draw off speed no loss of quality arises.